Cosmetic dermatologist Dr. Simon Ourian has worked on several, if not all, the Kardashian-Jenner sisters, and revealed to Khloe what he likes about working with each of them.The Keeping Up With the Kardashians star interviewed the doctor for her website, and straight up asked him if there was a sister he preferred. "You are very dedicated to anything you are involved in," he told Khloe, 31. "You are intrigued by all the new and exciting things we can do and I love the transformation you have had with all your own hard work and a little help from me."Dr. Ourian also called out Kim Kardashian West for her professionalism. "Kim is very detail-oriented and knows exactly what she wants and needs," he shared. "So when I work on her, it is like working with a colleague and I really enjoy it."

Kylie Jenner has praised Dr. Ourian for being "super natural about" her temporary lip injections, and he too seems pleased with the 18-year-old reality star's transformation. "Kylie has become very wise in what she wants to have done," he said of the youngest Jenner sister. "And she has been going through an amazing metamorphosis over the past couple of years."When ET sat down with Dr. Ourian, he touted that he has more and more clients wanting to look like Kylie and Kim. "For a long time people wanted to have Jessica Alba's lips," he dished. "Now it's Kylie Jenner's lips, Kim Kardashian's butt."